Laser scanning projectors constructed from microelectromechanical system (MEMS) components can be relatively small, and therefore implemented into easily portable devices such as picoprojectors. These laser scanning projectors can be used to display fixed or moving video images on a screen, wall, lens (in the case of a smartglass wearable), or user's skin (in the case of a smartwatch wearable). Since modern digital media is often in a high definition format, it is desirable for such laser scanning projectors to be capable of image display in high definition.
In general, MEMS laser scanning projectors function by optically combining red, green, and blue laser beams to form an RGB laser beam, and then directing the RGB laser beam to either a bi-axial mirror, or a set of two uni-axial mirrors working in tandem, with one of the axes being a fast axis and the other axis being a slow axis. The mirror or mirrors are controlled so as to linearly move at a constant rate along a slow axis, or “scan” the laser in a series of vertically spaced apart horizontal lines at a rate of speed such that the human eye perceived a complete image.
However, particularly in the case of laser scanning projectors, as the keystone angle (the angle between the RGB laser and normal to the plane of the target when the mirror or mirrors are at rest) angle increases, when the angle of incidence of the RGB laser beam on the screen changes as the scan proceeds through different vertically spaced apart horizontal lines, the use of a linear scan when the mirror is actuated at a constant angular speed provides for a non-uniform scan pattern and a non-constant movement speed of the beam spot on the target during the scan pattern. This can be seen in FIG. 1, in which the vertical spacing between the horizontal lines toward the top of the pattern is greater than the vertical spacing between horizontal lines toward the bottom of the pattern.
This results in the image formed having a non-constant vertical spatial resolution, which worsens image quality. In addition, this results in uneven image brightness, which further worsens image quality.